Spin mapping of intralayer antiferromagnetism and field-induced spin reorientation in monolayer CrTe2

A question then arises of how do strongly overlapped interlayer wave functions affect interlayer magnetism and whether there are any generalized spin-exchange coupling mechanisms solely for such a noncovalent interaction. The interlayer differential charge density shows that the interlayer electron coupling of of CrX₂(X = S, Se, Te) systems is significantly stronger than that of CrI₃. It is expected that different interlayer magnetic coupling mechanisms exist in CrX₂. The bulk phase of this kind of material shows ferromagnetism, and many studies speculate that the single layer should also be the ferromagnetic ground state. However, the theoretical prediction of the researchers found that the single layer of this kind of material is striped antiferromagnetic ground state. The in-plane magnetic orders of CrX₂ mono and few layers are tunable between striped antiferromagnetic (sAFM) and ferromagnetic (FM) orders by manipulating charge transfer between Cr t2g and eg orbitals. Such charge transfer is realizable through interlayer coupling, direct charge doping, or substituting S with Cl atoms^[1,2].

However, due to the fact that antiferromagnetic orders usually do not exhibit macroscopic magnetic moments, experimental detection is very difficult, and the antiferromagnetic ground state of CrX₂(X=S,Se,Te) materials mentioned in the above theoretical prediction are still lacking of experimental evidence in the two-dimensional limit. By combining spin polarised scanning tunnelling microscopy and first-principles calculations, we investigate the magnetism of vdW ML CrTe₂, which has been successfully grown through molecular-beam epitaxy. We observe a stable antiferromagnetic (AFM) order at the atomic scale in the ML crystal, whose bulk is ferromagnetic, and correlate its imaged zigzag spin texture with the atomic lattice structure. confirming the theoretical prediction of the researchers (FIG. 1 c). Previous studies of two-dimensional magnetic materials usually assumed that the material’s easy magnetization axis was along the conventional lattice base vector or out of plane direction. The researchers calculated that the magnetic moment direction of the CrTe₂ single layer was in the y-z plane at an Angle of 70 degrees from the z direction (FIG. 1 d), resulting in a novel spin reorientation transition mode under magnetic field (FIG. 1 e-g). The real space intrinsic antiferromagnetic order discovered and confirmed in this study, the magnetic order transformation in the single-layer limit, and the spin reorientation under external magnetic fields have not been previously reported before^[3].